[lammps-users] Apply background implicit solvent

Dear lammps users,
I am doing a simulation of membrane filtration based on lammps with granular pair style. Wanna share some of my understanding below, could some experienced friends please help me check whether I misunderstand the contents or not?

  1. As the fluid phase of the feed solution contains too many solvent particles, so the fix lb/fluid may not be proper because it has to include all the solvents. It will take too long.
  2. Right now I am using “fix viscous+velocity gaussian” as a way to apply the damping force and Brownian motion on the solute particles. Is this a good way to do it, any other forces that I missed in the system?
  3. I read the manual, another way is "fix langevin". With this fix langevin command, does this include all the forces of the implicit solvent?
    Besides, the fix viscous+velocity gaussian is no longer needed, otherwise, there will be repeated force.
  4. Any other ways of implementing the solvent in the system? any good examples for understanding?
    Best Regards

the most part of what you are asking for is about the science of your research and not about LAMMPS, so I have to refer you to discussing with your adviser/supervisor, more experienced colleagues (that are knowledgeable in your specific field of research) and the published literature. there will be plenty of discussions on implicit solvents and how to realize them.

as for LAMMPS, using fix langevin is effectively equivalent to using fix viscous plus a “random noise heater” that exactly compensates the amount of kinetic energy removed by the friction. the amount of friction is determined by the choice of time constant. using this is a rather crude model of an implicit solvent. if you want to know more about this, you should look it up in textbooks and the literature.

i am not aware of a more sophisticated implicit fluid model available in LAMMPS.